G
George B
- Jan 1, 1970
- 0
I recently attached a phototransistor to an audio amplifier (simple 4
stage transistor) after reading about observing ("listening") to
fluctuations in the light levels in the sky with such a device. If the light
is collected through a telescope one can "listen" to the light reflected off
clouds and the horizon. My amplifier, although it didn't have a great enough
gain to hear anything in the dark, made what sounded like white noise when a
torch light was directed onto the phototransistor.
Can anyone explain this considering that the filament is fed directly from a
battery(supposedly purely DC)? Could the noise be arising from radio
interference or could it be due to the nature of the electrochemical action
within the battery?
Before anyone suggests that something may have been amiss with my amplifier
I can assure you it was correctly biased and was able to amplify the 50Hz
mains hum from the lighting within the house quite nicely (the noise
disappeared if the photodiode was covered or taken outside in the dark).
Incandescent lights produce a soft hum, whilst fluorescent lights produce a
very loud and harsh 50Hz beat.
If I have time I might observe the waveform produced from the flashlight
using an oscilloscope.
I plan on getting either some higher gain transistors or building an IC
based amp to get the required gain in order to listen to fluctuations in the
light levels in the night sky.
George
stage transistor) after reading about observing ("listening") to
fluctuations in the light levels in the sky with such a device. If the light
is collected through a telescope one can "listen" to the light reflected off
clouds and the horizon. My amplifier, although it didn't have a great enough
gain to hear anything in the dark, made what sounded like white noise when a
torch light was directed onto the phototransistor.
Can anyone explain this considering that the filament is fed directly from a
battery(supposedly purely DC)? Could the noise be arising from radio
interference or could it be due to the nature of the electrochemical action
within the battery?
Before anyone suggests that something may have been amiss with my amplifier
I can assure you it was correctly biased and was able to amplify the 50Hz
mains hum from the lighting within the house quite nicely (the noise
disappeared if the photodiode was covered or taken outside in the dark).
Incandescent lights produce a soft hum, whilst fluorescent lights produce a
very loud and harsh 50Hz beat.
If I have time I might observe the waveform produced from the flashlight
using an oscilloscope.
I plan on getting either some higher gain transistors or building an IC
based amp to get the required gain in order to listen to fluctuations in the
light levels in the night sky.
George